Comparison of oxoperoxophosphatotungstate phase transfer catalysis with methyltrioxorhenium two-phase catalysis for epoxidation by hydrogen peroxide

Onium salts such as Q(3)[PO4{W2O2(mu-O-2)(2)(O-2)(2)}(2)] of Q(2)[HPO4{W2O2 (mu-O-2)(2)(O-2)(2)}] (Q(+) = [N(n-C6H13)(4)](+), [{(C18H37) 75% + (C16H33) 25%](2)N(CH3)(2)](4) (Arquad 2HT(R)), etc.) are effective under phase tran sfer catalysis (PTC) conditions for selective epoxidation of alkanes. Assoc iations of the corresponding anionic species and of other unidentified salt s under PTC conditions with Arquad were found to be as active and selective as the two-phase system CH3ReO3 (MTO)/H2O2-H2O/CH2Cl2. A P-31-NMR study sh ows several species which may imply breaking of the peroxo-bridged dimetall ic {W2O2(mu-O-2)(2)(O-2)(2)] units; they may be the key for understanding t he activity in catalytic epoxidation of cyclooctene, oct-1-ene, (R)-(+)-lim onene, alpha-pinene, (-)-beta-citronellene, Delta-3-carene, etc. These syst ems can compete in terms of yields and turnover numbers with two-phase syst ems involving MTO of its analogues with H2O2-H2O/Ch(2)Cl(2) and a proton sp onge for the synthesis of moderately sensitive epoxides. (C) 2000 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.